Copy between USB share and 'normal' share is going over LAN?

So I was thinking that the files are sent over the LAN instead that the readynas sees that the files are coming from the USB-HDD and it should not be going over the LAN back to where it's coming from, the readynas. This means that it didn't makes sense to copy it to an external USB-HDD. Moving from my laptop to the readynas over LAN gives the same result (qua duration). Can anyone confirm this?

Yes, doing a Windows copy or move between any two shares on the NAS, USB or otherwise, will go form the NAS over the ethernet through the Windows PC and back to the NAS. You see, Windows doesn't know the two volumes are on the same device.

The best way to copy directly from USB to the NAS, you need to set up a backup job. If you only want to do specific files and don't want to have to put them in a separate directory to distinguish them to the backup process, you could use an add-on like Xplorer. Unfortunately, if it's a SPARC based NAS, you won't find the direct copy to be much faster than the Windows copy, assuming you have gigabit ethernet; especially for an NTFS formatted USB drive.

This means that it didn't makes sense to copy it to an external USB-HDD. Moving from my laptop to the readynas over LAN gives the same result (qua duration).

If you only access to the files from the laptop, you are correct that leaving the USB drive connected to the laptop is likely better. It is certainly faster.